Daytime eating prevents mood vulnerability in night work

Shift workers have a 25 to 40% higher risk of depression and anxiety, with mental health disorders contributing to an estimated global cost of ∼US$1 trillion/y in lost workforce productivity alone (1,2). Shift workers often experience a misalignment between the central circadian clock and daily environmental/behavioral cycles, and circadian misalignment can negatively affect mood and emotional well-being in nonshift workers and shift workers (3–5). The identification of this important modifiable factor highlights the urgent need for evidence-based circadian interventions to prevent mood vulnerability in this at-risk population. Daytime eating—despite mistimed sleep—can maintain internal circadian alignment and prevent glucose intolerance during simulated night work (6). As impaired glycemic control is a risk factor for mood disruption (7), we tested the prediction that daytime eating prevents mood vulnerability, despite simulated night work. We performed a parallel-design randomized clinical trial (i.e., different participants randomly allocated to one of two meal timing groups) that included a 14-d circadian laboratory protocol with healthy participants (12 men, 7 women; age: 26.5 ± 4.1 y) (Fig. 1 A and B). Participants underwent a forced desynchrony (FD) protocol in dim light (∼3 lx) for 4 “days” of 28 h, such that each 28-h FD day resulted in an additional 4-h misalignment between the central circadian clock and external behavioral/environmental cycles. By the fourth FD day (simulated night work), participants were 12-h misaligned compared to the first FD day (baseline). In the daytime and nighttime meal control (DNMC) group, participants had a typical 28-h FD protocol, i.e., with behavioral and environmental cycles (sleep/wake, rest/activity, supine/upright posture, dark during scheduled sleep /dim light during wakefulness, etc.) scheduled on a 28-h cycle, including the fasting/eating cycle. Hence, meals occurred during both the daytime and nighttime, which is typical among night workers. In the daytime-only meal intervention (DMI) group, participants underwent a modified 28-h FD protocol with behavioral/environmental cycles scheduled on a 28-h cycle except for the fasting/eating cycle, which was scheduled on a 24-h cycle, thus resulting in meals consumed only during the daytime. We assessed depression-like and anxiety-like mood, which correspond to an amalgam of mood states typically observed in depression and anxiety, every hour during the 4 FD days using computerized visual analogue scales (VAS) (8) (SI Appendix).